1. Field of the Invention
The present invention relates to a nuclear magnetic resonance (NMR) spectrometer equipped with an NMR probe operating at cryogenic temperatures and, more particularly, to a device for attaching and detaching an NMR probe to and from an NMR spectrometer.
2. Description of Related Art
An NMR spectrometer is an instrument for analyzing the molecular structure of a sample by placing the sample to be investigated in a strong static magnetic field, applying RF electromagnetic waves to the sample to induce nuclear magnetic resonance, detecting an electrical signal (i.e., an NMR signal) induced as electric power in a detection coil by nuclear spins starting to precess, and obtaining an NMR spectrum.
A probe used in an NMR spectrometer has the detection coil inside it. The probe is replaceably mounted in a magnet generating a static magnetic field such that the detection coil is placed within the static magnetic field. RF electromagnetic waves are applied to the sample by the detection coil. Also, an NMR signal emanating from the sample is detected by the detection coil. One type of probe developed recently has a detection module having a detection coil and a preamplifier which are cooled by a refrigerant in order that NMR signals can be detected with higher sensitivity.
This type of probe capable of detecting NMR signals with high sensitivity by cooling the detection module is referred to as a “cryogenic probe” and to be discriminated from ordinary probes involving no cooling.
It is preferable for NMR apparatus users to be able to select and use a desired probe such that optimum signal detection is possible depending on the properties of a sample and on information to be obtained.
For example, where the amount of the sample is small, it is desirable to select a probe having a detection coil whose detection sensitivity is optimized for a small-volume sample tube. On the other hand, with respect to a sample available in a sufficient amount, it is preferable to select a probe permitting use of a large-volume sample tube, for the following reason. Generally, detection sensitivity increases in proportion to the ratio of the volume of the sample to the volume of the coil, i.e., in proportion to the square root of a so-called filling factor, and increases in proportion to the square root of the volume of the sample.
For example, if one wants to know the bonding between a carbon site and surrounding hydrogen atoms to get a clue to the composition of a sample, it is preferable to select a probe specifically designed for observation of 13C nuclear spins under irradiation of 1H nuclear spins. On the other hand, if one wants to investigate nitrogen sites and phosphorus sites in addition to carbon sites, it is desirable to select a probe having capabilities of making observations over a wide range permitting multinuclear NMR spectroscopy under irradiation of 1H nuclear spins.
In this way, if an optimum probe is selected according to the properties of a sample and information to be obtained and is used, then high-sensitivity measurements are possible. The time taken to obtain a spectrum having a desired signal to noise ratio by performing accumulations and averaging is reduced. Consequently, high measurement throughput can be accomplished.
Even where the measurement time is shortened by the use of such an optimum probe, if the time taken to exchange the current probe by an optimum probe and to make preparations for a measurement is long, then the total time required for the measurement is long. This will become a factor deteriorating the throughput.
In the case of an ordinary probe having no cooling means, the time taken to exchange the current probe is sufficiently short compared with the measurement time. Furthermore, a measurement can be started immediately after the end of the exchange work. Therefore, no great problems take place. However, in the case of a cryogenic probe, it takes longer to replace it than in the case of an ordinary probe. In addition, cooling and vacuum pumping sequence are required from the exchange to the time when the equipment is made usable. Therefore, it takes a long time to exchange the cryogenic probe. Consequently, it is inevitable that the total time taken to perform a measurement including the probe exchange time will be prolonged.